Curable fluoropolyether rubber compositions

ABSTRACT

A curable fluoropolyether rubber composition comprising (A) a straight-chain fluoropolyether compound having at least two alkenyl groups and a perfluoropolyether structure backbone, (B) an organosilicon compound having at least two silicon atom-bonded hydrogen atoms, which all form H—SiCH 2 — structures, and (C) a hydrosilylation catalyst cures into parts which have good heat resistance, chemical resistance, solvent resistance, parting property, water repellency, oil repellency and weather resistance as well as improved acid and alkali resistance and are useful as sealants.

[0001] This invention relates to curable fluoropolyether rubbercompositions which cure into parts having good water repellency, oilrepellency, heat resistance, solvent resistance, chemical resistance,weather resistance and parting property as well as improved acidresistance.

BACKGROUND OF THE INVENTION

[0002] Japanese Patent No. 2,990,646 (JP-A 8-199070) discloses acomposition comprising (A) a straight-chain fluoropolyether compoundhaving at least two alkenyl groups in a molecule and a perfluoroalkylether structure in the backbone, (B) an organosilicon compound having atleast two H—SiOSi structures in a molecule, and (C) a hydrosilylationcatalyst, which cures into parts having a good profile of heatresistance, chemical resistance, solvent resistance, parting property,water repellency, oil repellency and weather resistance.

[0003] Although this fluoropolyether rubber composition performs well inmost applications, a need for higher acid resistance exists in specialapplications associated with semiconductors, engine oils and the likewhere acid resistance is necessary.

SUMMARY OF THE INVENTION

[0004] An object of the invention is to provide curable fluoropolyetherrubber compositions which cure into parts having good heat resistance,chemical resistance, solvent resistance, parting property, waterrepellency, oil repellency and weather resistance as well as improvedacid resistance.

[0005] It has been found that by compounding (A) a straight-chainfluoropolyether compound having at least two alkenyl groups in amolecule and a perfluoropolyether structure in the backbone, (B) anorganosilicon compound having in a molecule at least two siliconatom-bonded hydrogen atoms, which all form H—SiCH₂— structures, and (C)a hydrosilylation catalyst, there is obtained a curable fluoropolyetherrubber composition which cures into parts having good heat resistance,chemical resistance, solvent resistance, parting property, waterrepellency, oil repellency and weather resistance as well as improvedacid resistance.

[0006] Fluoropolyether rubber compositions using an organosiliconcompound having H—SiOSi structures as disclosed in Japanese Patent No.2,990,646 are not so strong against acid since the SiOSi linkage canundergo silicon-oxygen cleavage under the action of acid. By contrast,in the organosilicon compound having H—SiCH₂— structures, thesilicon-carbon bond is highly stable against acid. Thus use of theorganosilicon compound having H—SiCH₂— structures provides afluoropolyether rubber composition with excellent acid resistance.

[0007] Accordingly the invention provides a curable fluoropolyetherrubber composition comprising

[0008] (A) a straight-chain fluoropolyether compound having at least twoalkenyl groups in a molecule and a perfluoropolyether structure in thebackbone,

[0009] (B) an organosilicon compound having in a molecule at least twosilicon atom-bonded hydrogen atoms, which all form H—SiCH₂— structures,and

[0010] (C) a hydrosilylation catalyst.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] Component (A) of the curable fluoropolyether rubber compositionaccording to the invention is a straight-chain fluoropolyether compoundhaving at least two alkenyl groups in a molecule and a divalentperfluoroalkyl ether structure in the backbone.

[0012] The perfluoroalkyl ether structure may be a structure comprisinga multiplicity of recurring units:

[0013] —C_(d)F_(2d)O— wherein d in each unit is independently an integerof 1 to 6, for example, a structure of the following general formula(5):

(C_(d)F_(2d)O)_(q)  (5)

[0014] wherein q is an integer of 1 to 500, preferably 2 to 400, nd morepreferably 10 to 200.

[0015] The recurring units —C_(d)F_(2d)O— constituting the structure offormula (5) are exemplified by the following units:

—CF₂O—,

—CF₂CF₂O—,

—CF₂CF₂CF₂O—,

—CF(CF₃)CF₂O—,

—CF₂CF₂CF₂CF₂O—

—CF₂CF₂CF₂CF₂CF₂CF2O—, and

—C(CF₃)₂O—.

[0016] Of these, —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O— and —CF(CF₃)CF₂O— areespecially preferred. It is noted that the perfluoroalkyl etherstructure may be comprised of such recurring units of one type or acombination of two or more types.

[0017] The alkenyl groups in the straight-chain fluoropolyether compound(A) are preferably those groups having 2 to 8 carbon atoms, especially 2to 6 carbon atoms, and terminated with a CH₂═CH— structure, for example,vinyl, allyl, propenyl, isopropenyl, butenyl, and hexenyl. Of these,vinyl and allyl are preferred. The alkenyl groups may be located at anyposition within the molecule, but preferably attached to opposite endsof the molecular chain. In this preferred arrangement, the alkenylgroups may be attached to opposite ends of the straight-chainfluoropolyether compound backbone directly or through a divalent linkinggroup: —CH₂—, —CH₂O— or —Y—NR—CO—. Herein Y is —CH₂— or a group of thefollowing structural formula (Z):

[0018] (wherein the free valence bond may be at the o, m or p-position),and R is hydrogen, methyl, phenyl or allyl.

[0019] The fluoropolyether compound (A) is preferably a straight-chainone of the following general formula (2) or (3).

CH₂═CH—(X)_(p)—Rf⁰—(X)_(p)—CH═CH₂  (2)

CH₂═CH—(X)_(p)—Q—Rf⁰—Q—(X)_(p)—CH═CH₂  (3)

[0020] Herein X is independently —CH₂—, —CH₂O— or —Y—NR′—CO— wherein Yis —CH₂— or a group of the following structural formula (Z):

[0021] (o, m or p-position), and R′ is hydrogen, methyl, phenyl orallyl. Rf⁰ is a divalent perfluoropolyether structure, preferably of theformula (5), that is, (C_(d)F_(2d)O)_(q). Letter p is independently 0or 1. Q is a divalent hydrocarbon group of 1 to 15 carbon atoms whichmay contain an ether bond, for example, an alkylene group or an alkylenegroup containing an ether bond.

[0022] Of these straight-chain fluoropolyether compounds (A), those ofthe following general formula (4) are preferred.

[0023] Herein X is independently —CH₂—, —CH₂O— or —Y—NR′—CO— wherein Yis —CH₂— or a group of the following structural formula (Z):

[0024] (o, m or p-position), and R′ is hydrogen, methyl, phenyl orallyl. Letter p is independently 0 or 1, r is an integer of 1 to 6, u isan integer of 2 to 6, and m and n each are an integer of 0 to 200.

[0025] Desirably the straight-chain fluoropolyether compounds of formula(4) have a weight average molecular weight of about 4,000 to 100,000,more desirably about 1,000 to 50,000.

[0026] Illustrative, non-limiting, examples of the straight-chainfluoropolyether compounds of formula (4) are given below. In theformulas, m and n are as defined above.

[0027] In the practice of the invention, to tailor the straight-chainfluoropolyether compound of formula (4) to a weight average molecularweight desired for a particular purpose, it is possible that thestraight-chain fluoropolyether compound be previously subjected tohydrosilylation reaction with an organosilicon compound having two SiHgroups in a molecule by a conventional method under ordinary conditionsto form a chain-extended product, which can be used as component (A).

[0028] Component (B) serves as a crosslinking agent and chain extenderfor component (A). Any desired organosilicon compound may be used aslong as it has at least two silicon atom-bonded hydrogen atoms in amolecule in which every silicon atom-bonded hydrogen atom forms anH—SiCH₂— structure. The organosilicon compound is preferably of thefollowing general formula (1).

[0029] Herein c is 1, 2, 3 or 4. R is a monovalent hydrocarbon group of1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, and may be thesame or different. Z is hydrogen or —Q—M, —Q—Rf, —Q—, —Rf′— or —Q—Rf′—Q—wherein Q is a divalent hydrocarbon group of 1 to 15 carbon atoms whichmay contain an ether bond, Rf is a monovalent perfluoroalkyl orperfluorooxyalkyl group, and Rf′ is a divalent perfluoroalkylene orperfluorooxyalkylene group. Letter s is 1, 2 or 3, t is 0, 1, 2 or 3,and a and b each are 0 or 1, with the proviso that a and b are not 0 atthe same time.

[0030] The hydrocarbon groups represented by R will be described laterin detail. Examples of Q include alkylene groups such as methylene,ethylene, propylene and hexylene, and those alkylene groups whose chainis separated by an ether bond (—O—). The monovalent perfluoroalkyl andperfluorooxyalkyl groups represented by Rf and the divalentperfluoroalkylene and perfluorooxyalkylene groups represented by Rf′will also be described later in detail.

[0031] Illustrative examples of the organosilicon compound are givenbelow. In the formulas, Me is methyl.

[0032] In consideration of compatibility with and dispersibility incomponent (A) and uniformity after curing, there may be used thoseorganosilicon compounds having at least one monovalent perfluoroalkyl,monovalent perfluorooxyalkyl, divalent perfluoroalkylene or divalentperfluorooxyalkylene group in a molecule.

[0033] The perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene andperfluorooxyalkylene groups are exemplified by those of the followinggeneral formulas.

[0034] Monovalent perfluoroalkyl

C_(g)F_(2g+1)—

[0035] g is an integer of 1 to 20, preferably 2 to 10.

[0036] Divalent perfluoroalkylene

—C_(g)F_(2g)—

[0037] g is an integer of 1 to 20, preferably 2 to 10.

[0038] Monovalent perfluorooxyalkyl

[0039] n is an integer of 1 to 5.

[0040] Divalent perfluorooxyalkylene

[0041] The sum of m+n is an integer of 1 to 200.

—(CF₂O)_(m)—(CF₂CF₂O)_(n)—CF₂—

[0042] Each of m and n is an integer of 1 to 50.

[0043] These perfluoro(oxy)alkyl and perfluoro(oxy)alkylene groups maybe attached to silicon atoms either directly or through divalent linkinggroups. Such divalent linking groups are alkylene and arylene groups andcombinations thereof, which may have an intervening bond such as anether bond-forming oxygen atom, amide bond, carbonyl bond or the like.Illustratively, divalent linking groups having 2 to 12 carbon atoms arepreferred, examples of which are given below.

—CH₂CH₂—

—CH₂CH₂CH₂—

—CH₂CH₂CH₂OCH₂—

—CH₂CH₂CH₂—NH—CO—

—CH₂CH₂CH₂—N(Ph)—CO—

—CH₂CH₂CH₂—N(CH₃)—CO—

—CH₂CH₂CH₂—O—CO—

[0044] Note that Ph is phenyl.

[0045] In addition to the monovalent organic group containing a mono- ordivalent fluorinated substituent, that is, perfluoroalkyl,perfluorooxyalkyl, perfluoroalkylene or perfluorooxyalkylene group, theorganosilicon compound (B) has the silicon atom-bonded monovalentsubstituent R, which is selected from substituted or unsubstitutedhydrocarbon groups of 1 to 20 carbon atoms. Exemplary hydrocarbon groupsare alkyl groups such as methyl, ethyl, propyl, butyl, hexyl,cyclohexyl, octyl and decyl, alkenyl groups such as vinyl and allyl,aryl groups such as phenyl, tolyl and naphthyl, aralkyl groups such asbenzyl and phenylethyl, and substituted ones of the foregoing groups inwhich some hydrogen atoms are substituted with chlorine atoms, cyanogroups or the like, such as chloromethyl, chloropropyl and cyanoethyl.

[0046] With respect to the organosilicon compound, the number of siliconatoms per molecule is usually about 2 to about 60, preferably about 3 toabout 30, though not limited thereto.

[0047] The following examples are also typical of the organosiliconcompounds. They may be used alone or in admixture of two or more. Notethat Me is methyl and Ph is phenyl.

[0048] An appropriate amount of component (B) blended is such that 0.5to 5 mol, especially 1 to 2 mol of hydrosilyl groups (or SiH groups) incomponent (B) are available per mol of alkenyl groups (e.g., vinyl,allyl and cycloalkenyl) in component (A). Less amounts of component (B)may achieve an insufficient degree of crosslinking whereas excessiveamounts of component (B) may allow chain lengthening to becomepreferential, inviting short curing and foaming, and aggravating heatresistance, compression set and the like.

[0049] Component (C) is a hydrosilylation catalyst, which is typicallyselected from transition metals, for example, platinum group metals suchas Pt, Rh and Pd and compounds of these transition metals. Because thesecompounds are generally expensive noble metal compounds, the inventionfavors the use of platinum compounds which are readily available.

[0050] Exemplary platinum catalysts are chloroplatinic acid, complexesof chloroplatinic acid with olefins such as ethylene, and complexes ofchloroplatinic acid with alcohols and vinylsiloxane, as well as platinumon silica, alumina and carbon, though not limited thereto.

[0051] Platinum group metal compounds other than the platinum compoundsinclude rhodium, ruthenium, iridium and palladium compounds, forexample, RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, RhCl(C₂H₄)₂, Ru₃(CO):₁₂,IrCl(CO)(PPh₃)₂, and Pd(PPh₃)₄ wherein Ph is phenyl.

[0052] The amount of the catalyst used is not critical and a catalyticamount may achieve a desired curing rate. From the economical standpointand to obtain satisfactory cured parts, the catalyst amount ispreferably about 0.1 to 1,000 ppm, more preferably about 0.1 to 500 ppmof platinum group metal based on the entire curable composition.

[0053] In addition to component (B), the curable composition of theinvention may have another crosslinking agent and chain extender forcomponent (A). Specifically, an organosilicon compound having in amolecule at least two SiH structures not corresponding to component (B),typically H—Si—OSi structures, may be blended for ease of working andtailoring rubber physical properties. Such a SiH-bearing organosiliconcompound not corresponding to component (B) is not critical as long asit has at least two SiH groups in a molecule. It may have a chain,cyclic or network structure.

[0054] Where an organosilicon compound having hydrosilyl groups or SiHgroups is added as a crosslinking agent and chain extender for component(A) in addition to component (B), the amount of this additionalorganosilicon compound is preferably such that the total amount of SiHgroups (available from component (B) and additional organosiliconcompound) is 0.5 to 5 mol, especially 1 to 2 mol per mol of alkenylgroups (e.g., vinyl, allyl and cycloalkenyl) in component (A). Lessamounts of SiH groups may achieve an insufficient degree of crosslinkingwhereas excessive amounts of SiH groups may allow chain lengthening tobecome preferential, inviting short curing and foaming, and aggravatingheat resistance, compression set and the like.

[0055] The proportion of component (B) to the additional organosiliconcompound having SiH structures is not critical and may be set asappropriate depending on a particular application.

[0056] If desired, various additives may be added to the inventivecurable composition for improving its practical usage. For instance,polysiloxanes containing CH₂═CH(R)SiO units wherein R is hydrogen or asubstituted or unsubstituted monovalent hydrocarbon group (see JP-B48-10947) and acetylene compounds (see U.S. Pat. No. 3,445,420 and JP-B4-3774) are added for the purpose of controlling the curing rate of thecurable compositions. Other useful additives are ionic compounds ofheavy metals (see U.S. Pat. No. 3,532,649).

[0057] To the curable composition of the invention, fillers may be addedfor the purposes of reducing thermal shrinkage upon curing, reducing thecoefficient of thermal expansion of the cured elastomer, improvingthermal stability, weather resistance, chemical resistance, flameretardance or mechanical strength, and/or lowering the gas permeability.Exemplary additives include fumed silica, quartz flour, glass fibers,carbon, metal oxides such as iron oxide, titanium oxide and ceriumoxide, and metal carbonates such as calcium carbonate and magnesiumcarbonate. If desired, suitable pigments and dyes are added.

[0058] The method of preparing the curable composition according to theinvention is not critical. The composition may be prepared simply bymixing the above-described components. The composition may be formulatedas two parts, one part consisting of component (A) and components (B)and (C) and the other part consisting of components (A) and (C), whichare to be combined together on use. For the composition to cure, roomtemperature cure is possible depending on the type of functional groupin component (A) and the type of catalyst (C) although a common,preferred practice is to heat the composition at about 100° to 200° C.for several minutes to several hours for curing.

[0059] On use, depending on its particular application and purpose, thecurable composition may be dissolved in a suitable fluorochemicalsolvent, for example, 1,3-bistrifluoromethylbenzene or perfluorooctanein a desired concentration before it is applied.

[0060] The curable fluoropolyether rubber composition cures into partswhich have good heat resistance, chemical resistance, solventresistance, parting property, water repellency, oil repellency andweather resistance as well as improved acid and alkali resistance. Thecomposition is thus useful in a variety of molding applications, forexample, as sealants for semiconductor manufacturing apparatus, O-rings,diaphragms and sealants for automobiles and aircraft, roll materials forcopiers, and constituent materials for secondary cells and fuel cells.

EXAMPLE

[0061] Examples of the invention are given below by way of illustrationand not by way of limitation. The viscosity is a measurement at 25° C.All parts are by weight.

Example 1

[0062] To 100 parts of a polymer of formula (i) below (viscosity 8,500cs, average molecular weight 22,000, and vinyl content 0.009 mol/100 g)was added 20 parts of dimethylsiloxy-treated fumed silica having aspecific surface area of 200 m²/g. They were mixed, heat treated andmilled on a three-roll mill. To the mixture were added 2.64 parts of afluorinated organosilicon compound of formula (ii) below, 0.2 part of atoluene solution of a catalyst in the form of chloroplatinic acidmodified with CH₂═CHSiMe₂OSiMe₂CH═CH₂ (platinum concentration 1.0 wt %),and 0.4 part of a 50% toluene solution of ethynyl cyclohexanol. Theywere mixed to give composition I. It was deaerated in vacuum, placed ina rectangular frame of 2 mm deep, deaerated again, and press cured at100 kg/cm² and 150° C. for 10 minutes. From the cured sample, a specimenwas cut out and measured for physical properties according to JIS K-6251and 6253. The results are shown below. Hardness (Durometer type A)  40Elongation 540% Tensile strength  10.7 MPa

[0063] The specimen was also examined for heat resistance, chemicalresistance, solvent swell, low-temperature property and moisturepermeability. The results are shown in Table 1 to 5.

Comparative Example 1

[0064] Composition II was prepared as in Example 1 except that 2.49parts of a fluorinated hydrogensiloxane of formula (iii) was usedinstead of the fluorinated organosilicon compound of formula (ii). As inExample 1, a cured sheet was obtained from composition II. A specimenwas cut therefrom and measured for physical properties according to JISK-6251 and 6253. The results are shown below. Hardness (Durometer typeA)  41 Elongation 620% Tensile strength  11.8 MPa

[0065] The specimen was also examined for chemical resistance, with theresults shown in Table 2. TABLE 1 Heat resistance (200° C.) Initial 3days 7 days Hardness (Durometer type A) 40  39  38 Elongation (%) 540500 (−7%) 450 (−17%) Tensile strength (MPa) 10.7  8.9 (−17%)  6.7 (−37%)Heat loss (%) —  1  1.9

[0066] TABLE 2 Chemical resistance (Change of rubber hardness) Example 1Comparative Example 1 Composition I Composition II Surface SurfaceChemical Hardness state Hardness state Initial 40 — 41 — Conc. 42 (+2)unchanged 48 (+7) unchanged hydrochloric acid Conc. 39 (−1) unchanged 40(−1) deteriorated sulfuric acid Conc. 39 (−1) unchanged 30 (−11)deteriorated hydrofluoric acid Trifluoroacetic 38 (−2) unchangeddecomposed decomposed acid 40% aqueous 41 (+1) unchanged 41 (+0)unchanged KOH solution

[0067] It is evident from Table 2 that composition I has superior acidresistance to composition II. TABLE 3 Solvent swell (volume change %)Solvent Composition I Viton GFLT FE61 gasoline +10 +5 +42 methanol +2+16 +1 chloroform +12 +12 +23 acetone +7 +148 +177 toluene +7 +10 +30IPA +4 +1 +1 acetonitrile +1 +46 +3 MEK +15 +150 +194 ethyl acetate +13+150 +172 THF +18 +149 +204 n-hexane +7 +2 +18 carbon tetrachloride +10+4 +27

[0068] TABLE 4 Low-temperature property (German torsion test)Composition I Viton E-60 KE951 T₂ −36° C.  −6° C. −41° C. T₅ −47° C.−11° C. −43° C. T₁₀ −53° C. −14° C. −44° C. T₁₀₀ −61° C. −20° C. −50° C.

[0069] TABLE 5 Moisture permeability (CUP method) Sample Moisturepermeability Composition I 4 KE951 100  Viton GFLT 4 FE251 50 

Example 2

[0070] A composition was prepared as in Example 1 except that a polymerof formula (iv) (viscosity 5,300 cs, average molecular weight 17,000,and vinyl content 0.012 mol/100 g) was used instead of the polymer offormula (i) and the amount of the fluorinated organosilicon compound waschanged to 3.53 parts. As in Example 1, a cured sheet was obtained fromthis composition. A specimen was cut therefrom and measured for physicalproperties according to JIS K-6251 and 6253. The results are shownbelow. Hardness (Durometer type A)  45 Elongation 420% Tensile strength 10.2 MPa

[0071] The specimen was also examined for chemical resistance, with theresults shown in Table 6.

Example 3

[0072] A composition was prepared as in Example 1 except that 100 partsof a polymer of formula (v) (viscosity 136,000 cs, average molecularweight 23,300, and vinyl content 0.008 mol/100 g) was used instead ofthe polymer of formula (i) and the amount of the fluorinatedorganosilicon compound was changed to 2.30 parts. As in Example 1, acured sheet was obtained from this composition. A specimen was cuttherefrom and measured for physical properties according to JIS K-6251and 6253. The results are shown below. Hardness (Durometer type A)  35Elongation 540% Tensile strength  11.2 MPa

[0073] The specimen was also examined for chemical resistance, with theresults shown in Table 6.

Example 4

[0074] A composition was prepared as in Example 1 except that 100 partsof a polymer of formula (vi) (viscosity 87,000 cs, average molecularweight 27,900, and vinyl content 0.007 mol/100 g) was used instead ofthe polymer of formula (i) and the amount of the fluorinatedorganosilicon compound was changed to 1.95 parts. As in Example 1, acured sheet was obtained from this composition. A specimen was cuttherefrom and measured for physical properties according to JIS K-6251and 6253. The results are shown below. Hardness (Durometer type A)  35Elongation 530% Tensile strength  10.2 MPa

[0075] The specimen was also examined for chemical resistance, with theresults shown in Table 6.

Example 5

[0076] A composition was prepared as in Example 1 except that 1.69 partsof the fluorinated organosilicon compound of formula (ii) and 0.46 partof a fluorinated organosilicon compound of formula (vii) were usedtogether. As in Example 1, a cured sheet was obtained from thiscomposition. A specimen was cut therefrom and measured for physicalproperties according to JIS K-6251 and 6253. The results are shownbelow. Hardness (Durometer type A)  55 Elongation 380% Tensile strength 9.7 MPa

[0077] The specimen was also examined for chemical resistance, with theresults shown in Table 7.

Example 6

[0078] A composition was prepared as in Example 1 except that 2.47 partsof a fluorinated organosilicon compound of formula (viii) were usedinstead of the fluorinated organosilicon compound of formula (ii). As inExample 1, a cured sheet was obtained from this composition. A specimenwas cut therefrom and measured for physical properties according to JISK-6251 and 6253. The results are shown below. Hardness (Durometer typeA)  37 Elongation 640% Tensile strength  9.3 MPa

[0079] The specimen was also examined for chemical resistance, with theresults shown in Table 7.

Example 7

[0080] To 100 parts of the polymer of formula (i) (viscosity 8,500 cs,average molecular weight 22,000, and vinyl content 0.009 mol/100 g) usedin Example 1 was added 20 parts of dimethylsiloxy-treated fumed silicahaving a specific surface area of 200 m²/g. They were mixed, heattreated and milled on a three-roll mill. To the mixture were added 1.06parts of the fluorinated organosilicon compound of formula (ii) used inExample 1, 1.51 parts of the fluorinated hydrogensiloxane of formula(iii) used in Comparative Example 1, 0.2 part of a toluene solution of acatalyst in the form of chloroplatinic acid modified withCH₂═CHSiMe₂OSiMe₂CH═CH₂ (platinum concentration 1.0 wt %), and 0.4 partof a 50% toluene solution of ethynyl cyclohexanol. They were mixed togive a composition. It was deaerated in vacuum, placed in a rectangularframe of 2 mm deep, deaerated again, and press cured at 100 kg/cm² and150° C. for 10 minutes. From the cured sample, a specimen was cut outand measured for physical properties according to JIS K-6251 and 6253.The results are shown below. Hardness (Durometer type A)  41 Elongation590% Tensile strength  12 MPa

[0081] The specimen was also examined for chemical resistance, with theresults shown in Table 7. TABLE 6 Example 2 Example 3 Example 4 SurfaceSurface Surface Chemical Hardness state Hardness state Hardness stateInitial 45 — 35 — 35 — Conc. 48 (+3) unchanged 39 (+4) unchanged 37 (+2)unchanged hydrochloric acid Conc. 43 (−2) unchanged 30 (−5) unchanged 33(−2) unchanged sulfuric acid Conc. 42 (−3) unchanged 26 (−9) unchanged32 (−3) unchanged hydrofluoric acid Trifluoroacetic 41 (−4) unchanged 24(−11) unchanged 32 (−3) unchanged acid 40% aqueous KOH 47 (+2) unchanged41 (+6) unchanged 38 (+3) unchanged solution

[0082] TABLE 7 Example 5 Example 6 Example 7 Surface Surface SurfaceChemical Hardness state Hardness state Hardness state Initial 55 — 37 —41 — Conc. 57 (+2) unchanged 38 (+1) unchanged 44 (+3) unchangedhydrochloric acid Conc. 54 (−1) unchanged 36 (−1) unchanged 40 (−1)unchanged sulfuric acid Conc. 53 (−2) unchanged 36 (−1) unchanged 37(−4) unchanged hydrofluoric acid Trifluoroacetic 52 (−3) unchanged 36(−1) unchanged 35 (−6) deteriorated acid 40% aqueous 58 (+3) unchanged38 (+1) unchanged 41 (0) unchanged KOH solution

[0083] It is evident from Tables 2, 6 and 7 that the curablefluoropolyether rubber compositions using H—SiCH₂— type organosiliconcompounds in Examples show excellent acid resistance as compared withthe similar composition using an H—SiOSi type organosilicon compound inComparative Example. Example 7 demonstrates that a combination ofH—SiCH₂— and H—SiOSi types is also effective for improving acidresistance.

[0084] Japanese Patent Application No. 2000-196789 is incorporatedherein by reference.

[0085] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A curable fluoropolyether rubber composition comprising (A) astraight-chain fluoropolyether compound having at least two alkenylgroups in a molecule and a perfluoropolyether structure in the backbone,(B) an organosilicon compound having in a molecule at least two siliconatom-bonded hydrogen atoms, which all form H—SiCH₂— structures, and (C)a hydrosilylation catalyst.
 2. The composition of claim 1 whereincomponent (B) is an organosilicon compound of the following generalformula (1):

wherein c is 1, 2, 3 or 4, R is a monovalent hydrocarbon group of 1 to20 carbon atoms and may be the same or different, Z is hydrogen or —Q—M,—Q—Rf, —Q—, —Rf′— or —Q—Rf′—Q— wherein Q is a divalent hydrocarbon groupof 1 to 15 carbon atoms which may contain an ether bond, Rf is amonovalent perfluoroalkyl or perfluorooxyalkyl group, Rf′ is a divalentperfluoroalkylene or perfluorooxyalkylene group, s is 1, 2 or 3, t is 0,1, 2 or 3, and a and b each are 0 or 1, with the proviso that a and bare not 0 at the same time.
 3. The composition of claim 1 whereincomponent (A) is a straight-chain fluoropolyether compound of thefollowing general formula (2) or (3):CH₂═CH—(X)_(p)—Rf⁰—(X)_(p)—CH═CH₂  (2)CH₂═CH—(X)_(p)—Q—Rf⁰—Q—(X)_(p)—CH═CH₂  (3)wherein X is independently —CH₂—, —CH₂O— or —Y—NR′—CO— wherein Y is—CH₂— or a group of the following structural formula (Z):

(o, m or p-position), and R′ is hydrogen, methyl, phenyl or allyl, Rf⁰is a divalent perfluoropolyether structure, p is independently 0 or 1,and Q is a divalent hydrocarbon group of 1 to 15 carbon atoms which maycontain an ether bond.
 4. The composition of claim 3 wherein component(A) is a straight-chain fluoropolyether compound of the followinggeneral formula (4):

wherein X is independently —CH₂—, —CH₂O— or —Y—NR′—CO—wherein Y is —CH₂—or a group of the following structural formula (Z):

(o, m or p-position), and R′ is hydrogen, methyl, phenyl or allyl, p isindependently 0 or 1, r is an integer of 1 to 6, u is an integer of 2 to6, and m and n each are an integer of 0 to 200.